At least 30 civilians were killed when the US bombed several drug-making facilities in western Afghanistan in May, a UN agency said in a report Wednesday, though the US military immediately disputed the findings.

The United Nations Assistance Mission in Afghanistan (UNAMA) conducted an investigation over four months looking into what happened May 5 when the US military bombed dozens of sites it had identified as Taliban methamphetamine labs.

In a statement, UNAMA said it had ‘verified 39 civilian casualties (30 deaths, five injured and four undetermined), including 14 children and one woman, due to the 5 May air strikes’.

The agency went on to say that it had also received ‘credible information’ about an additional 30 deaths -- mostly women and children -- and was working to further verify these claims.

‘In addition to imagery collection during the precision strikes, USFOR-A conducted exhaustive assessments of the facilities and surrounding areas after the strikes,’ the command said in a statement.

‘Combined assessments determined the strikes did not cause deaths or injuries to non-combatants.’

The US military in 2017 and early 2018 carried out multiple strikes against Taliban opium processing plants, but the efforts had little impact on the insurgents' revenue stream and were unpopular among Afghan farmers, many of whom rely on the poppy crop.

The military then switched its focus to the more lucrative meth industry.